Annealing furnace



July 28, 1931.

N. G. GlRsHowlTcH 1,816,253

ANNEALING FURNACE Filed OCT.. 3. 1930 ATTORN EY' Patented July 28, 1931 UNITED STATES PATENT OFFICE NAUM G. GIRSHOWITCH, F NEW YORK, N. Y.

ANN EALIN G- FURNACE Application led October 3, 1930. Serial No. 486,184.

a furnace composed of different. sections,

each section especiallyv suitable for one particular portion of the temperature curve.

For instance, when annealing cast iron castings for converting them into malleable iron, it is necessary to subject them to four successive heat treatments as follows:

l. Gradually raisi'ngthe temperature to a maximum at which disintegrat-ion of the cementite takes place.

2. Maintaining the maximum temperature fora certain length of time until the cementite disintegration is completed.

3. More or less rapid cooling until a suitable temperature is reached for disintegrating perlite into a more uniform structure.

4. Maintaining this temperat-ure for a certain length of time.

There are two principal types of malleable iron furnaces: tunnel or continuous furnaces, and periodic furnaces, preferably with electric heating. In the latter type of furnace the Work is loaded in a batch and is subjected to the heat treatment until the process is completed, when the Work is Withdrawn.

The tunnel furnaces or kilns are very economical, the fuel consumption being low, in

case of coal equal to about 20% by Weight of castings. These furnaces are Well adapted for various temperature curves, although it is difficult to maintain the desired temperatures very accurately and uniformly throughout the sections of the furnace. For this reason these furnaces are not so Well adapted forproduction of very high grade -castings for Which an exact temperature control 1s necessary. Another disadvantage of these furnaces is that their efciency becomes considerably reduced for light load onthe kiln cars and it becomes more diilicult to maintain a uniform temperature curve with only partly lled cars. Besides, they occupy a 5,0 large amount of space inthe plant, the time Athe annealing process are carried in a corof treatment-being controlled by the length of the furnace.

Periodic furnaces, mainly of the electric type, are very Well adapted for maintaining very l accurately the required temperature 55 curve, with a uniform heating throughout the furnace, so that it is possible to obtain in such furnaces the highest grades of malleable iron. The exact temperature control can be easily adjusted for various loads, and eo the furnace itself occupies very little room in the plant. Its fuel consumption is, however, rather high, reaching 400 kilowatt hours per ton of castings, or, expressing in terms of coal, about 1000 lbs. of coal per ton, or 65 rIhe actual experience hasshoWn that for the production of the highest grades of malleable iron it is necessary to maintain a very accurate temperature onlyV during the last period of annealing, when perlite becomes disintegrated and a granular structure of metal develops. The other three periods do not require such an exact temperature control. It appears -therefore that it is possible to build a composite furnace so as to combine 76 the advantages of the two types of furnaces and to eliminate their disadvantages.

I found that for this purpose the best results are obtained if the first two stages of respondingly shortened tunnel furnace, of a sufficient length only'to complete the disintegration of cementite. The subsequent cool ing can be carried rapidly and it does not require any furnace, as the Work can be simply S5 exposed to the air dra-ft until its temperature reaches the point when perlite begins to disintegrate. Then the Work canbe placed in a periodicl or additional (separate) electric furnace where the temperature 'is maintained constant all the time and Within required limits to obtain the -fine granular structure of the metal. The Work remains in the furnace until the process is completed.

My arrangement permits to use a tunnel furnace for the greatest part of the thermal process, thereby obtaining the benefit of the economic operation of such a furnace, saving, however, in its cost and space requirements; the final annealing, at the same time, .Een

is carried in the separate furnace under the most exact temperature control.

My invention is more fully described in the accompanying specification and drawings in Which- Fig. 1 is a plan view of my composite furnace, Fig. 2 'is a sectional elevation of Same,

and Fig. 3 is a temperature curve for malleable iron.

My furnace comprises atunnel portion 1 of an ordinary construction except that it is shortened and terminates with the firing zone 2 where burners 3 are located. The hot gases flow through the preheating portion 1 into a stack 4. Rails 5 pass through the tunnel for cars 6 carrying castings or other articles to be annealed. A hydraulic plunger' 7 is used to push the cars through the tunnel. Any other suitable device, of course, can be employed for this purpose.

The rails 5 extend beyond the tunnel and pass under a cooling hood 8 with a stack 9 through which the air is drawn by any suitable means, for instance, by a fan or by natural draft. The rails terminate at a pit 10 of an electric furnace 11 and are in alignment with rails 12 on a lift table 13 and with eX- tension rails 14 on the other sideof the pit.

The electric furnace may have one or several compartments 15 lined with a suitable refractory material and provided with electric heating elements 16 connected by cables 17 with a source of electric current. The number of compartments 15 is selectedl so as to provide for a continuous operation of the furnace in accordance withv the operation of the tunnel kiln.

The lift table 13 is mounted on a'ram 18 operated hydraulically in a cylinder 19 and is adapted to raise the cars into the furnacesA l5 where they are retained in a suspended position by retaining lugs 20 of an ordinary construction.

The operation of my furnace is as follows.

I'n the reheating portion 1 of the tunnel furnace t e castings 21 on .the cars 6 are brought to. a temperature of about 17 00 F. during from 24 to 36 hours, following the portion 22 of the temperature curve Fig. 3. In the firing zone the castings are maintained at this temperature for about 24 hours. l

This period corresponds to the portion 23 of the temperature curve. The castings are then removed from the furnace and are placed under the cooling hood 8 Where they are cooled following the curve 24. This cooling may be quite rapid as it does not affect the quality of the product.

The cars are then brought one at a time on the table 13 and raised into the corresponding furnace compartment 15, beting held in a raised position by lugs or latches 20. Here the temperature is maintained at the grade of the product (see curve 25, Fig. 3).

With this arrangement it is possible 'to reduce the total length of the tunnel furnace by about 3/5 times, with corresponding reduction of the first cost and maintainance expenses. The number of electric furnaces will be reduced,.and the total power consumption, expressing in terms of coal, will be about 25% of the Weight of metal to be annealed. The whole installation will be considerably shorter .than it would be required if a tunnel furnace alone was used (about 200 feet instead of 350 for 50 tons of castings in 24 hours).

I claim as my invention:

1. In an annealing furnace, the combination with a tunnel kiln, cars for work adapted to pass through said tunnel kiln, said kiln containing preheating and high temperature Zones and terminating at the end of said high temperature zone, and a separate furnace adapted to maintain a constant temperature and containing several cells for said cars, the number of said cells being proportioned according to the time required for final heat treatment and to the time interval between successive arrivals of said cars from said tunnel kiln.

2. In an annealing furnace, the combination with a tunnel kiln, rails passing through said kiln, cars for' W'ork to be annealed adapted to pass through said kiln on said rails, said kiln containing preheating and high temperature zones and terminating at the end of said high temperature zone, (a cooling arrangement for cars coming from said kiln, said rails extending through said cooling arrangement, a separate furnace in a coordination with said kiln and said cooling arrangement, said separate furnace con-v taining compartments for said cars vand adapted to maintain a. constant temperature, and means to selectively place said cars in said compartments.

In testimony whereof I affix my signature.

NAUM Gr. GIRSHOWITCI-I.

from 1200 to 1450 degrees F. for a length of time depending on the kind of castings and 

